A write head such as an LED (Light Emitting Diode) head is used in an electrophotographic image forming apparatus such as a digital multi-function peripheral (MFP), printer, and facsimile machine and is positioned and attached with a predetermined interval from a photoreceptor drum to achieve high-quality images.
However, it is difficult to assemble mass-produced image forming apparatuses such that intervals between the write heads and the photoreceptors become completely the same, and some variance is generated at the time of assembly. Therefore, the position of the write head must be adjusted in each apparatus after the assembly such that the interval between the write head and the photoreceptor falls within a certain tolerance to achieve images with a predetermined quality.
Therefore, in a conventional electrophotographic image forming apparatus such as an MPF, a mechanism adjusting the position of the LED head is disposed in a main body of the image forming apparatus. In a manufacturing line of the image forming apparatus, a photoelectric transducer such as a CCD is mounted on the photoreceptor mounting position and an adjustment work is performed by detecting an LED exposure spot shape from the CCD output and using a dedicated jig for adjusting the LED head position.
On the other hand, in electrophotographic image forming apparatuses, photoreceptors are consumables, and a variance is generated in a distance between the photoreceptor surface and the LED head due to an individual difference of the photoreceptor mounting position. A lens built into the LED head has a focal depth of only ±0.1 mm, and if the variance exceeds the focal depth, a desired image quality cannot be acquired unless focus adjustment is performed such that the focal point of the light emitted from the LED head conforms to the photoreceptor surface after replacing the photoreceptor.
Since the apparatus of the above dedicated jig is large and expensive, the dedicated jig cannot be used when a service person visits a customer's site to adjust the LED head position, and since the position is adjusted by performing test print and visually checking printed line widths, this operation takes a long time and adjustment accuracy is low in reality.
In view of the above situations, a clamshell image forming apparatus is known which can be opened at a lower portion of the LED head. Since the clamshell image forming apparatus can be opened at the lower portion of the LED head, when positioning the write head and the photoreceptor drum with a predetermined distance, the mounting position of the write head can easily be adjusted.
Japanese Laid-Open Patent Publication No. 2001-130047 discloses a technology of reducing a focal shift generated when correcting a position shift of a scanning line in an electrophotographic recording apparatus using an LED head by bring a contact rod into contact with a photoreceptor surface to maintain a constant distance between the LED head and the photoreceptor surface. Japanese Laid-Open Patent Publication No. 2003-173073 discloses a technology capable of adjusting a distance between a writing head and a photoreceptor drum, and the scanning inclination of the writing head relative to the photoreceptor drum from the side portion of a main body apparatus.
If a user must replace consumables or adjust parts in the electrophotographic image forming apparatuses during use, a skilled “service man” performs the operation. Conventionally, it has been insisted that the maintenance by a service man must be shifted to “user maintenance”, and the “user maintenance” is introduced in the case of a portion of parts, for example, a process kit, since the printing quality is not deteriorated and the apparatus is not damaged even when a user replaces the parts. However, in the case of parts that are a core of the electrophotographic mode, the operation is dependent on the “service man maintenance”.
Especially, with regard to the mounting adjustment of image writing members such as an optical unit and LED head using laser light which has an influence on the print quality, the operation is regarded as an essential item of the “service man maintenance”, not only since a lot of skill is required to perform dot diameter adjustment using a print image at a mounting site after the adjustment of the image forming apparatus at the time of factory shipment but also from a standpoint of having an influence on the print quality. The mounting adjustment of image writing members such as an optical unit and LED head must be performed every time an electrostatic latent image support (photoreceptor) is replaced in addition to the above maintenance and, since the adjustment operation is difficult, the adjustment has been omitted at the time of the replacement of the photoreceptor in a normal process.
In recent years, print resolution is increased from conventional 300 dpi to 600 and 1200 dpi as higher quality images are formed by image forming apparatuses, and it is difficult even for a skilled service man to respond such increment with the conventional adjustment technique. For reference, in the case of 1200 dpi, a dot diameter of one dot is generally 12 to 13 μm, which cannot be recognized.
Due to eccentricity, deformation, diameter variance, etc., of the photoreceptor drum including the photoreceptor, a distance between the write head and the photoreceptor is changed depending on a rotation angle. Therefore, if the interval adjustment is performed at a position where the distance is maximized between the write head and the photoreceptor, the distance between the write head and the photoreceptor drum becomes too small at other positions; contrary, if the interval adjustment is performed at a position where the distance is minimized between the write head and the photoreceptor, the distance between the write head and the photoreceptor drum becomes too large at other positions; and in either case, the optimum interval adjustment cannot be performed.
When adjusting the interval between the write head and the photoreceptor, if a line extended from a regulating member is shifted such that the line does not intersect with a center line of the drum rotation axis, i.e., if the position of the regulating member is shifted from the photoreceptor drum in the sub-scanning direction, the shape of the exposure spot applied to the photoreceptor does not become a perfect circle and a sharp latent image cannot be formed on the photoreceptor.